There have been known pigments that can emit phosphorescence visible in a dark place for relatively long time (afterglow) after irradiated by sunlight or light from artificial lighting and repeatedly show such characteristics. These pigments absorb light energy in a light place and emit phosphorescence in a dark place like charge and discharge of storage battery, and called as phosphorescent pigments. There have also been known luminous pigments that comprise a phosphorescent pigment and a radioactive substance such as tritium, .sup.147 Pm and .sup.226 Ra, where radioactive ray emitted by the radioactive substance stimulates the phosphorescent pigment to emit phosphorescence.
Such phosphorescent pigments and luminous pigments are currently used for various products utilizing their long afterglow characteristics, for example, switches, lights for carrying, articles for use in darkroom, handrails, luminous indications such as wall indications, guidance signs, escape tools, other phosphorescent indications such as phosphorescent safety marks, ornamental articles such as ash trays, earrings and tablecloths, printed matter, toys, stationery and the like. For example, as uses of the phosphorescent pigments, Japanese Patent Unexamined Publication No. Hei 4-51405 (JP-A-51405/92) discloses phosphorescent wall panels for escape corridor, Japanese Patent Unexamined Publication No. Hei 1-111075 (JP-A-111075/89) discloses phosphorescent fibers, Japanese Patent Unexamined Publication No. Hei 1-200388 (JP-A- 200388/89) discloses light emitting ropes, and Japanese Patent Unexamined Publication No. Hei 1-200389 (JP-A-200389/89) discloses phosphorescent sheets for indications.
Such products as mentioned above may be desired to be colored depending on their uses while maintaining the long afterglow characteristics.
However, when the conventional phosphorescent pigments are colored, their phosphorescence luminance is substantially reduced depending on color and color strength. For example, according to JIS K 5120, Commentary of Phosphorescent Pigments, Commentary p.5, "Commentary List: Drop of Phosphorescence Luminance of Phosphorescent Pigments by Coloration", the phosphorescence luminance of such pigments is reduced to, considering the luminance when not colored as 100%, 15.7% when colored in green (added amount: 3.6%), 14.1% when colored in reddish orange (added amount: 2.4%) or 5.1% when colored in red (added amount: 9.1%). Thus, reddish orange or red coloration reduces the phosphorescence luminance more significantly.
To solve the above problem, for example, Japanese Patent Unexamined Publication No. Hei 3-166269 (JP-A-166269/91) discloses colored phosphorescent pigments and luminous pigments comprising organic pigments. However, phosphorescence luminance of these colored phosphorescent pigments and luminous pigments is still quite low because their phosphorescence luminance is not enhanced, and their color variation has substantial limitation.
Nevertheless, as products and commercial needs are more diversified, articles exhibiting long afterglow characteristics with high phosphorescence luminance and being colored in various colors have been highly desired.
For example, articles exhibiting afterglow characteristics in metallic color such as gold and silver or in black have not been practically used yet, because phosphorescence cannot be obtained by a combination of phosphorescent pigment and metallic color pigment or black pigment. This is because a layer containing a metallic color pigment or black pigment exhibits poor light transmission and hence a phosphorescent pigment contained therein cannot store light energy.
By the way, phosphorescent phosphors exhibiting higher phosphorescence luminance compared to conventional phosphorescent pigments have been developed (Japanese Patent Unexamined Publication No. Hei 7-11250 (JP-A-11250/95)). However, these phosphorescent phosphors themselves still cannot solve the above problem. The reduction of phosphorescence caused by mixing with a colored pigment is still too high to substantially enable coloration in metallic color such as gold and silver or in black.
The present invention has been completed to solve these problems, and an object of the present invention is to provide a composite exhibiting long afterglow characteristics which can exhibit higher phosphorescence luminance and color tone comparable to conventional ones with respect to the colors conventionally used for coloration of such materials such as red and green, and an article utilizing such a composite exhibiting long afterglow characteristics.
Another object of the present invention is to provide a composite exhibiting long afterglow characteristics which is in a color conventionally impossible to be used for the coloration of such materials, for example, metallic color such as gold and silver, black or the like, and can exhibit sufficient phosphorescence luminance, and an article utilizing such a composite exhibiting long afterglow characteristics.